Koen Verbist

Seasonal Predictability of Daily Rainfall Characteristics in Central Northern Chile for Dry-Land Management

Abstract The seasonal predictability of daily winter rainfall characteristics relevant to dry-land management was investigated in the Coquimbo region of central northern Chile, with focus on the seasonal rainfall total, daily rainfall frequency, and mean daily rainfall intensity on wet days at the station scale. Three approaches of increasing complexity were tested. First, an index of the simultaneous El Nino–Southern Oscillation (ENSO) was regressed onto May–August (MJJA) observed precipitation; this explained 32% of station-averaged rainfall-amount variability, but performed poorly in a forecasting setting. The second approach used retrospective seasonal forecasts made with three general circulation models (GCMs) to produce downscaled seasonal rainfall statistics by means of canonical correlation analysis (CCA). In the third approach, a nonhomogeneous hidden Markov model (nHMM) driven by the GCM’s seasonal forecasts was used to model stochastic daily rainfall sequences. While the CCA is used as a downsc...

Hydro-meteorological trends in semi-arid north-central Chile (29–32°S): water resources implications for a fragile Andean region

Abstract Changes in hydro-meteorological historical records are of considerable importance for future planning. This study analyses trends of hydro-climatological indices of annual and seasonal precipitation, temperature and discharge in the “Norte Chico” region of Chile (29–32°S), located in the Central Andes. It addresses how these trends possibly impacted on the water resources in a nival regime, typical for arid mountainous regions. Homogenous records were tested against monotonic trends using the non-parametric rank-based Mann-Kendall test. The results suggested, at a very high confidence level, a strong warming signal trend over recent decades, consistent at the annual and seasonal levels. Furthermore, warmer days are observed in summer, especially at higher elevations. The region also experienced a shift in the rainy season over the last 42 years. However, an increase in precipitation was observed over recent decades, whereas an annual decrease was the general tendency when the whole century was considered. Changes in discharge were not unequivocal and glacier retreat has been compensated for possibly by an increase in snowmelt in recent years. Hence, in an under-studied area, from the hydrological perspective, this work provides some insights for a better understanding of changing hydrological processes in the mid-latitude Andes Cordillera. Editor Z. W. Kundzewicz Citation Souvignet, M., Oyarzún, R., Verbist, K.M.J., Gaese, H. and Heinrich, J., 2012. Hydro-meteorological trends in semi-arid north-central Chile (29–32°S): water resources implications for a fragile Andean region. Hydrological Sciences Journal, 57 (3), 479–495.

Bias Adjustment of Satellite‐based Precipitation Estimation using Gauge Observations—A Case Study in Chile

Author(s): Yang, Z; Hsu, K; Sorooshian, S; Xu, X; Braithwaite, D; Verbist, KMJ | Abstract:

Climate risk management for water in semi–arid regions

BackgroundNew sources of hydroclimate information based on forecast models and observational data have the potential to greatly improve the management of water resources in semi-arid regions prone to drought. Better management of climate-related risks and opportunities requires both new methods to develop forecasts of drought indicators and river flow, as well as better strategies to incorporate these forecasts into drought, river or reservoir management systems. In each case the existing institutional and policy context is key, making a collaborative approach involving stakeholders essential.MethodsThis paper describes work done at the IRI over the past decade to develop statistical hydrologic forecast and water allocation models for the semi arid regions of NE Brazil (the “Nordeste”) and central northern Chile based on seasonal climate forecasts.ResultsIn both locations, downscaled precipitation forecasts based on lagged SST predictors or GCM precipitation forecasts exhibit quite high skill. Spring-summer melt flow in Chile is shown to be highly predictable based on estimates of previous winter precipitation, and moderately predictable up to 6 months in advance using climate forecasts. Retrospective streamflow forecasts here are quite effective in predicting reductions in water rights during dry years. For the multi-use Oros reservoir in NE Brazil, streamflow forecasts have the most potential to optimize water allocations during multi-year low-flow periods, while the potential is higher for smaller reservoirs, relative to demand.ConclusionsThis work demonstrates the potential value of seasonal climate forecasting as an integral part of drought early warning and for water allocation decision support systems in semi-arid regions. As human demands for water rise over time this potential is certain to rise in the future.

EVALUATION OF THE USLE MODEL TO ESTIMATE WATER EROSION IN AN ALFISOL

The USLE model was evaluated to estimate water erosion in an Alfisol located in San Pedro, Metropolitan Region of Chile. Values of erosivity (R) obtained by using the Arnoldus approximation (MFI) and equations proposed by the Institute for Nature Conservation (ICONA) in Spain were adapted to the conditions in Chile. For the evaluation of soil loss, data were used for each precipitation event causing erosion during the period 1996-2000, obtained by measurements on experimental plots with treatments of subsoiling, infiltration trenches and natural prairie. They were compared with estimated values of erosion in terms of basic statistics and indices based on variance and regression. In the descriptive and comparative analysis of the selected equations, it was determined that soil losses estimated with USLE using the equation of rainfall erosivity by ICONA provided soil loss values which were well-adjusted to the values recorded in Chile, compared to erosivity calculated by the Arnoldus approximation (MFI) that overestimated the soil loss values. According to the results or estimates in this study it was concluded that the USLE model was capable of detecting the trend of the data, and resulted in estimates consistent with the pattern observed in the field data.

Merging high‐resolution satellite‐based precipitation fields and point‐scale rain gauge measurements—A case study in Chile

Author(s): Yang, Z; Hsu, K; Sorooshian, S; Xu, X; Braithwaite, D; Zhang, Y; Verbist, KMJ | Abstract:

Spatial mapping of drought in Zambia using regional frequency analysis

ABSTRACT Regional frequency analysis based on L-moments was applied to assess the spatial extent of meteorological droughts in tandem with their return periods in Zambia. Weather station monthly rainfall data were screened to form homogeneous sub-regions-, validated by a homogeneity criterion and fitted by a generalized extreme value distribution using goodness-of-fit test statistics. Predictor equations at regional scale for L-moment ratios and mean annual precipitation were developed to generate spatial maps of meteorological drought recurrences. The 80% of normal rainfall level and two thresholds of 60% and 70% were synonymous with moderate and severe droughts, respectively. Droughts were more severe in the south than in the north of Zambia. The return periods for severe and moderate droughts showed an overlapping pattern in their occurrence at many locations, indicating that in certain years droughts can affect the entire country. The extreme south of Zambia is the most prone to drought.